When referencing .NET types in your code, you can either use the fully-qualified namespace or only use the simplified name and omit the namespace if the simplified name can be resolved without ambiguity. For example, instead of typing System.String, you can simply type String provided that String is not used by any other class.
The editor provides a light bulb quick action, Simplify name Type, to automatically replace the fully-qualified name with the simplified name:
You can choose to simplify the current occurrence of a fully-qualified name, all occurrences of that name in the current file (click Document), or all occurrences in the current file and any copybooks displayed in the expanded copybook view in it (click Program).